1. Field of the Invention
The present invention relates in general to automotive automatic transmissions, and more particularly to a drum supporting structure installed in the automatic transmission for rotatably supporting an aluminum drum on an aluminum drum support. More specifically, the present invention is concerned with a bearing arrangement installed in the drum supporting structure, by which an undesired centrifugal whirling of the drum about the drum support is suppressed during rotation of the drum.
2. Description of the Prior
In automotive automatic transmissions of a type wherein an aluminum drum is rotatably supported by an aluminum drum support, various drum supporting structures have been hitherto proposed and put into practical use. One of them is such a structure as shown in FIG. 13.
That is, in such a conventional drum supporting structure, a first steel sleeve 104 is press-fitted in a larger diameter bore of the aluminum drum 103, a second steel sleeve 105 is press-fitted on a smaller diameter portion of the aluminum drum support 102 and a steel ring 111 is fitted to a raised wall of the drum support 102. Upon assembly, the first steel sleeve 104 is carried on three seal rings 102a, 102b and 102c mounted on a larger diameter portion of the drum support 102, the second steel sleeve 105 carries thereon a cylindrical inner wall of a smaller diameter bore of the drum 103, and the steel ring 111 bears an axial base end of the drum 103, as shown.
That is, in the illustrated conventional drum supporting structure, three steel members, which are the first and second steel sleeves 104 and 105 and the steel ring 111, are interposed between the aluminum drum support 102 and the aluminum drum 103. However, practical supporting of the aluminum drum 103 on the aluminum drum support 102 is carried out by only the second steel sleeve 105. That is, due to presence of the three seal rings 102a, 102b and 102c between the first steel sleeve 104 and the aluminum drum support 102, the first steel sleeve 104 does not participate in supporting the drum 103 on the drum support 102. That is, a so-called one point supporting is employed in the illustrated conventional drum supporting structure.
However, the one point supporting tends to bring about undesired centrifugal whirling of the drum 103 relative to the drum support 102 when the drum 103 rotates about the drum support 102. This phenomenon becomes much severe when the axial length of the drum 103 increases.
Furthermore, usage of the three steel members 104, 105 and 111 has brought about a time-consumed and troublesome assembling work. Particularly, fixing the steel ring 111 to the raised wall of the drum support 102 has needed a very skilled technique. These have caused a costly assemblage of the transmission. Furthermore, in such drum supporting structure, it has been difficult to feed a sufficient amount of lubrication oil to an end clearance 110 which inevitably appears between the drum support 102 and the drum 103 at a position between the first steel member 104 and the steel ring 111. In fact, even when an oil passage xe2x80x9cOxe2x80x9d is provided in the larger diameter portion of the drum support 102 to lubricate such end clearance 110 by using a lubrication oil flowing in a lubrication oil passage formed in an output shaft OUT, adequate oil feeding to the clearance 110 is not expected.
It is therefore an object of the present invention to provide a drum supporting structure for an automotive automatic transmission, which is free of the above-mentioned drawbacks.
According to the present invention, there is provided a drum supporting structure for use in an automatic transmission. The automatic transmission includes a transmission case, an aluminum drum support fixed to the transmission case, an aluminum drum rotatably held by the drum support, a piston installed in the drum, a hydraulic fluid passage formed in the drum to feed the piston with a hydraulic work, a lubrication oil passage formed in the drum support to feed the piston with a lubrication oil, and seal rings for hermetically separating the lubrication fluid passage and the lubrication oil passage. The drum supporting structure comprises larger and smaller diameter portions and a radially raised wall portion which are defined by the aluminum drum support, the radially raised wall portion being arranged at an axially base end of the larger diameter portion, the larger diameter portion having the seal rings concentrically mounted thereon; larger and smaller diameter bores defined by the aluminum drum to respectively receive therein the larger and smaller diameter portions of the drum support allowing an axially base end of the drum to face the radially raised wall portion of the drum support; a first steel sleeve coaxially fitted to a cylindrical inner wall of the larger diameter bore, the first steel sleeve including a cylindrical major portion which is slidably put on the seal rings and a cylindrical end portion which is slidably and directly supported on the larger diameter portion of the aluminum drum support, the cylindrical major portion and the cylindrical end portion being integrally connected to constitute a single unit; and a second steel sleeve coaxially fitted to a cylindrical outer wall of the smaller diameter portion of the drum support to bear a cylindrical inner wall of the smaller diameter bore of said drum.